Ahmad Abousamra, who has dual citizenship in the U.S. and Syria, left the country in 2006, the FBI said.

"There's no specific trigger for the timing of this. We just thought it was a good time in our investigation to share this information with the public -- both in United States and worldwide -- in hopes that a tipster will come forward," said Special Agent-In-Charge Richard DesLauriers.

Abousamra was indicted on terrorism charges in 2009 after taking multiple trips to Pakistan and Yemen to obtain military training for the purpose of killing American soldiers overseas, the FBI said.

Abousamra also traveled to Iraq with the hope of joining forces fighting against the United States, the FBI said.

The exact nature of his activities in Iraq is unknown, the FBI said.

"He received his degree from UMass Boston in computer science and he's worked in the telecommunications industry. He speaks Arabic and English fluently may be using those skills today," said Heidi Williams of the FBI.

The FBI said he may be living in Aleppo, Syria, with his wife, at least one child, a daughter, and extended family.

"We're using traditional media campaigns here in the United States, as well as using social media, Facebook, Twitter and YouTube worldwide," DesLauriers said.

A reward of up to $50,000 is being offered for information leading to his arrest.

Anyone with information is asked to contact the FBI by calling 1-800-CALL-FBI or 617-742-5533, via the Internet at https://tips.fbi.gov, or by calling their local FBI office, or the nearest U.S. Embassy or Consulate.